Incandescent lamps for automotive headlights like H1, H4, H7, H11 and similar halogen lamps are usually characterized by white light having a yellowish tint. Previous approaches to improve light quality to a more pure white were at the price of a reduced efficiency.
Examples of previous approaches are: DE102008033019A1 proposing an interference and/or absorption coating transmitting close to the maximum of the eye sensitivity, thus providing high color temperatures, but being silent on the material composition of the coating and its transmission efficiency; and U.S. Pat. No. 6,508,573B1 proposing various red absorbing metal oxides for a film on an incandescent lamp's glass bulb providing a color temperature of 4000 K for the lamp.